We report the preparation and characterization of a group of thermally stable silane-based copolymers prepared by radical polymerization of various phenylmaleimides with vinyl- or allyltrialkoxysilanes. These polymers exhibit thermal stability up to 400 °C or better, as determined by thermal analysis. Polymer preparation and stability (resistance to hydrolysis) were confirmed by FTIR, 1H NMR, and 13C NMR spectroscopy. Polymer molecular weights (5000 to 25 000 g mol−1) and polydispersity indices (1.87–3.06) were determined by gel permeation chromatography (GPC). While controlling the functional groups on the phenylmaleimide affords the tuning of the chemical properties of the resulting polymers, the choice of the alkoxysilane leads to control over the rate and extent of reactivity of the polymers. These materials are being employed in the design of thermally robust polymer–silica materials for use in high-temperature chromatography.